A navigation system for use in a vehicle includes a display device which is used when a route is to be determined, or a display device which is opened automatically or according to a driver's request when the vehicle is to be guided by the navigation system. When conditions for determining an optimum route are inputted into a route setting map to start the route search, a detailed map containing the route (i.e., a route search map) is displayed. When the search is completed, a whole route map (i.e., a wide-area map) is displayed in a form to permit the driver to clearly recognize the whole route. The driver can visually and aurally recognize from the whole route map that specific route to be travelled from the present location to the destination. After this, the driver pushes a guide start button to initiate the guidance by means of the navigation system.
Of course, the route may be missed by a wrong turn, even with such road guidance. In order to prevent this problem, there is disclosed in Japanese Patent Laid-Open No. 173815/1989, for example, a system having the ability to instantly inform the driver of a deviation, if any, from the route and to re-search a new route.
According to the method of the prior art, at the location where the driver recognizes that he or she has deviated from the initially determined route, he or she is guided by a newly searched route to the destination. If this new route can not be found, the driver is guided to return the vehicle to the intersection where he or she left the original route. This may require the driver to reverse the direction of travel 180.degree. so as to return to that location. Moreover, it takes a long time to search the new route and it may become necessary to stop the vehicle to wait for the new route search.